Change Of Open Circuit Potential Research Articles

Anodic oxidation of Co(II) complexes with amines on a rotating Au electrode: Ligand effects in relation to the application for autocatalytic metal deposition

For the comparison of the electrochemical activity of Co(II)–amine complexes, the electrochemical response of an Au rotating disk electrode in alkaline Co(II)–glycine solutions to six amines: ethylenediamine (en), propane-1,2-diamine (pn-1,2), propane-1,3-diamine (pn-1,3), cyclohexane-1,2-diamine (chn), butane-1,4-diamine (bn), diethylenetriamine (dien), was studied. Addition of amines tested (except for bn) in mM levels shifts the open-circuit potential to more negative values by up to 0.5 V and enhances dramatically the anodic Co(II) oxidation current, as a result of Co(II) complex transformation into more stable and electrochemically active Co(II)–amine species. The effect of amines on the open-circuit potential changes in the line: dien ∼ en > pn-1,2 ∼ chn > pn-1,3 ≫ bn, and on the anodic current in the sequence: dien ∼ en > pn-1,2 > chn > pn-1,3 ≫ bn. The procedure described helps to select ligands for Co(II) complexes used as reducing agents in electroless plating solutions. The amines of high electrochemical response: dien, en, pn-1,2, and possibly, chn, are suitable for electroless copper deposition, pn-1,3 (a lower response), for electroless silver deposition, and bn (no response), not suitable for electroless plating solutions.

Magnetic Field Effects on the Open Circuit Potential of Ferromagnetic Electrodes in Corroding Solutions

Magnetic fields shift the open circuit potential (OCP) of ferromagnetic electrodes (Fe, Co, and Ni) in corroding solutions. The OCP changes we observe (a) follow the series Fe>Co>Ni; (b) increase with the magnetic flux density; (c) reach a maximum with disk electrodes approximately 1 mm in diameter; and (d) depend on the orientation of the electrode. We report that when the surface of the electrode is oriented parallel (theta = 90 degrees) or perpendicular (theta = 0 degrees) to the magnetic field, the open circuit potential moves in opposite directions (positive and negative, respectively) with the largest changes occurring when the electrode surface is parallel to the magnetic field. Nonconvective sleeve electrodes produce the same behavior. The overall experimental evidence suggests that the magnetic field changes the OCP by modifying the surface concentrations of the paramagnetic participants in the corrosion process of the ferromagnetic electrode by species in solution; this in turn is accomplished by imposing a field-gradient driven mode of mass transfer upon paramagnetic species in solution (magnetophoresis). Simulations of the magnetic field around the ferromagnetic electrode at the two extreme orientations considered here show that in one case (theta = 90 degrees) field gradients actually repel, while in the other case (theta = 0 degrees) they attract paramagnetic species in the vicinity of the electrode.

Correlation between electrochemical characteristics and thermal stability of advanced lithium-ion batteries in abuse tests—short-circuit tests

The shutdown function of a separator is an important factor in the safety of advanced lithium-ion batteries (ALB). When a separator without proper shutdown function is used, battery safety would depend on the thermal stability of electrode materials. Results show that thermal stability of a battery, contributed from both the anode and cathode, decreases noticeably after cycling. DSC shows that exothermicity from SEI decomposition and the reaction of the lithiated graphite and electrolyte around 140 °C increases as cycle number increase; main reason is the gradual thickening of passivation film, observed through three-electrode ac impedance measurements. DSC also shows a similar trend of exothermicity for Li x CoO 2 cathode. The lesser the amount of lithium ( x-value) in Li x CoO 2, the larger the exothermicity and the lower the decomposition temperature. Using a three-electrode system to observe the changes of open-circuit potential in Li x CoO 2 cathode, thermal instability is a consequence of decreased lithium content as cycle increases.

Adsorption characteristics of albumin on gold and titanium metals in Hanks’ solution using EQCM

The adsorption of Bovine Serum Albumin (BSA) on gold and titanium surfaces in Hanks’ solution was monitored using the electrochemical quartz crystal microbalance (EQCM) technique. The changes in mass and open circuit potential at rest potential and mass and current at constant potentials were measured before and after the introduction of BSA.The mass of BSA adsorbed on titanium reached a steady value within one hour, while the albumin adsorbed on gold continued to increase. The amount of BSA adsorbed by titanium increased with concentration and stabilized at 0.8 mg/ml while that on gold did not stabilize. This indicates a monolayer of the protein on titanium and multi-layer on gold. The adsorption of BSA on gold and titanium was accelerated by the charge of potential.The time before stabilizing the adsorption‒desorption phenomena also increased with the BSA concentration.

Effect of velocity on corrosion characteristics of Al−Mg alloys

The electrochemical observation of AA 5083 alloy, which has been used as a structural material in high speed ship, was carried out in flow condition of 3.0% NaCl solution at 20°C through rotating disc type apparatus, which is easy to control flow velocity. As a result, it has been observed that the corrosion behavior of AA5083 alloy is affected by the changes in corrosion surface and hydrodynamic flow pattern transiting from laminar to turbulent flow. The surface oxide film was almost left in laminar condition (below 2000 rpm, Re≤1.7×105) and was disrupted partially due to the eddy flow in transition condition (at 3000 rpm, 1.7×105 Re≤3.5×105). The overall attack was observed by the removal of surface oxide film in turbulent condition (above 4000 rpm, Re≥3.5×105). It was also supported by the sharp change in open-circuit potential (OCP) and the changes in the anodic polarization behavior at transition region.

Potentiometric Responses of Poly(pyrrole) Films Surface Modified by Nafion

The influence of surface modification with Nafion layer on potentiometric characteristics of conducting polymer (CP) films was studied. In this article the possibility of inducing the permselective, cationic responses of both anion- and cation-exchanging layers is presented. From theoretical considerations it follows that the effect of coating of CP with permselective cation-exchanging layer on potentiometric responses of the bilayer system is exclusively dependent on the ion-exchanging properties of the inner phase. For the bilayer of two cation-exchanging films the cationic responses are expected, whereas for the anion-exchanging inner layer the open circuit potential changes will reveal the properties of modifying film, the CP will serve as an electrical signal transducer only. Experimental results obtained for poly(pyrrole) layers doped with chloride (PPyCl) and hexacyanoferrate(II) ions (PPyFeCN) are discussed. The polymer doped with a chloride ions is well-known anion-exchanging membrane, whereas the latter is a cation-exchanging one. Applying the cation exchanging, ion-conductive Nafion layer on the top of poly(pyrrole) results in an increase of slope of the characteristic recorded for PPyFeCN layer from 35.7 to 58.1 mV/dec, although the linear responses were in the latter case limited to the range from 2×10−5 to 2×10−3 mol/L, i.e., to the modifying layer permselectivity region. For PPyCl film the type of potentiometric characteristic was reversed from the anionic of slope −70.6 mV/dec to cationic 33.1 mV/dec, the cationic responses were observed within the concentration range from 10−5 to 2×10−3 mol/L. The results obtained point to exclusion anions from the ion-exchange process, which for PPyCl means the possibility of total reversing the anionic characteristic to the cationic one. The cationic selectivity of tested bilayer systems was compared.

Dilatometric and electrochemical measurements for studying hydrogen transport through oxide layers

Simultaneous dilatometric and electrochemical measurements are employed for studying the kinetic parameters and mechanism for hydrogen transport through metal oxides. As a model, CeO 2 layer on a palladium wire substrate is investigated. Hydrogen is dissolved in aqueous solutions where their acidity and the oxide layer thickness are the studied parameters. Based on both open circuit potential and length changes, it is deduced that molecular diffusion through pores and imperfections in the ceria lattice is the rate determining step and no chemical reactions are involved in the oxide bulk. The following diffusion coefficients are calculated by using a diffusional transport model: D (1 N KOH) =1.69×10 −11 cm 2 s −1D (1 N H 2 SO 4 )=1.72×10 −11 cm 2 s −1.

The modelled and observed transition from redox to ionic potentiometric sensitivity of poly(pyrrole)

One of the key problems in the application of conducting polymer membranes in the analytical ionic potentiometry is a high redox sensitivity of the polymer films, i.e. the open-circuit potential dependence on the solution redox potential. In this work the influence of the solution redox system charge transfer kinetics and its concentration on the observed ionic potentiometric responses of poly(pyrrole) films was investigated. In the theoretical considerations two different processes were distinguished: (a) spontaneous polymer charge/discharge process occurring due to irreversible redox reactions involving the polymer film and (b) fast charge transfer reactions with the redox system in solution. According to the model calculations, in the presence of a strongly irreversible redox couple in solution (e.g. O 2/H 2O) alteration of the electrolyte concentration is followed by polymer open-circuit potential changes, i.e. the typical ionic potentiometric calibrations are observed. On the other hand, for a fast redox system in the solution, the polymer open-circuit potential is constant and equal to the equilibrium potential of the redox couple. In the presence of both redox systems mentioned above, the potentiometric responses are affected by the concentration of redox reactants and a transition from typical ionic to pure redox response is observed. The above theoretical considerations are in good agreement with experimental results obtained for both anion and cation exchanging poly(pyrrole) films (doped with either chloride or hexacyanoferrate anions, respectively): (a) in the presence or absence of dissolved oxygen, (b) in the presence of deliberately added Fe(CN) 6 3−/4− or Fe(III)/Fe(II) redox systems.

Characterization of adsorption of glycine on gold and titanium electrodes using electrochemical quartz crystal microbalance

The adsorption of the simplest amino acid, glycine, on gold and titanium surfaces in Hanks’ solution was monitored using the quartz crystal microbalance. The changes in mass and open circuit potential at rest potential and mass and current at constant potentials were measured before and after the injection of glycine. Results showed a momentary adsorption of glycine, followed by the desorption of a part of glycine adsorbed. The adsorbed amount of glycine increased with the increase of glycine concentration. The time before stabilizing the adsorption–desorption phenomena also increased with the concentration. More glycine was adsorbed on titanium than on gold because of the difference in the surface electric charges. The adsorption was accelerated by the charge of potential.

A correlation between the changes in total charge and open circuit potential of a hydrogen electrode during the adsorption of neutral particles and the formation of adatoms from ions

Analytical descriptions are given for the charges passed through the hydrogen electrode (at E ads=const) and the shifts of its open circuit potential, which are observed during the strong adsorption of neutral particles and ions with the formation of adatoms. The integral values of transients of current and those of open circuit potential are explained by using the concept of electrode total charge. The interrelation between transients of current and open circuit potential is analyzed. To check experimentally the relationships obtained, the adsorption measurements on a platinum electrode in solutions of iodine and iodide anions are mainly used (0.5 M H 2SO 4 as the supporting electrolyte). The theoretical conclusions are shown to be in adequate agreement with the experimental results.

The influence of bacteria on the passive film stability of 304 stainless steel

The stability of stainless steel 304 in the presence of aerobic and anaerobic bacteria was investigated in a continuous flow system using electrochemical impedance spectroscopy and scanning electron microscopy (SEM) examinations. The results show that the open circuit potential (OCP) of stainless steel was ennobled (shifted in the electropositive direction) by about +150 mV in the presence of the aerobic bacteria. The observed change of OCP in the electropositive direction can be explained by an increase in the rate of the cathodic reaction. Also the presence of an aerobic biofilm led to a decrease in the polarization resistance of stainless steel is not only due to the growth of micropits, as shown from SEM micrographs, but also due to thinning of the passive film. In the presence of only Pseudomonas fragi, the electrochemical impedance response showed a capacitive behavior with RP on the order of 500 kΩ. The addition of anaerobic sulfate reducing bacteria (SRB) to the test medium decreased RP to 12 kΩ due to an increase in localized corrosion, as indicated by SEM examination.

Biological actions of synthetic locust ion transport peptide (ITP)

Locust Ion Transport Peptide (ITP) a member of the arthropod neuropeptide family which includes hyperglycemic, vitellogenesis-inhibiting, and moult-inhibiting hormones (CHH, VIH, MIH, respectively) was synthesized as proposed by Meredith et al. (1996)with terminal amidation of amino acid residue 72 and with 3 disulphide bridges. This is the first member of this family to be synthesized. Biological activities of synthetic ITP (synITP) were very similar to those previously reported for ITP purified from Schistocerca corpora cardiaca (ScgITP) and partially sequenced by Audsley et al. (1992a, b). Dose–response curves for both synITP and ScgITP on ileal transport of Cl − (measured as increased short-circuit current, Δ I sc), were similar with a EC 50 of 1–2 nM. The I sc time course and maximum Δ I sc across ileal epithelia at different dosages of synITP and ScgITP had similar patterns as did changes in transepithelial open-circuit potential ( V t) and resistance ( R t), reflecting changes in salt transport which drives fluid absorption. Disulphide bridges were shown to be required for biological activity of synITP, which caused the same 4-fold increase in ileal fluid transport rate ( J v) as previously reported for ScgITP. Both synITP and ScgITP caused only partial stimulation of rectal I sc and had no significant effect on rectal J v. These results indicate that the structure of ITP predicted earlier from cDNA is correct.

Self-discharge mechanism of Vanadium–Titanium metal hydride electrodes for Ni–MH rechargeable battery

In order to investigate the effect of the equilibrium hydrogen pressure (plateau pressure) of metal hydride (MH) alloys on self-discharge behavior, V 0.9Ti 0.1 alloys having multi-plateau pressures (low and high plateau pressures) have been used as working electrodes in a half cell. The thermal desorption experiment and open-circuit potential monitoring were conducted to observe the self-discharge behavior of the electrode. From the thermal desorption spectra of the fully charged and discharged V 0.9Ti 0.1 electrode (to −0.7 V versus Hg/HgO), it is found that only the higher one of the two plateau pressure regions of the V 0.9Ti 0.1 electrodes is electrochemically useful for battery application. But the open-circuit potential change and thermal desorption spectra of the V 0.9Ti 0.1 electrode after various open-circuit storage periods prove that the self-discharge behavior is attributed to the hydrogen desorption from the low plateau pressure (10 −8 atm) as well as the high plateau pressure (0.1 atm). Therefore, it is suggested that the self-discharge behavior of V 0.9Ti 0.1 electrodes can not be effectively suppressed by reducing the plateau pressure of alloys through alloy modification. In addition, the pressure–composition–isotherms ( P–C–T) of the low pressure region can be estimated by using the open-circuit potential corresponding to this region in Nernst's equation.

Self-discharge mechanism of vanadium-titanium metal hydride electrodesfor Ni-MH rechargeable battery

In order to investigate the effect of the equilibrium hydrogen pressure (plateau pressure) of metal hydride (MH) alloys on self-discharge behavior, V09Ti01 alloys having multi-plateau pressures (the low and high plateau pressure) have been used as working electrodes in a half cell. A thermal desorption experiment and open-circuit potential monitoring were conducted to observe the self-discharge behavior of the electrodes. From the thermal desorption spectra of fully charged and discharged V09Ti01 electrodes (to-0.7 V vs. Hg/ HgO), it was found that only the high plateau pressure region from V09Ti01 electrodes is electrochemically useful in battery application. However, the open-circuit potential change and thermal desorption spectra of V09Ti01 electrodes after various open-circuit storage periods prove that self-discharge behavior is caused by hydrogen desorption from the low plateau pressure region (10-8 atm) as well as the high plateau pressure region (0.1 atm). Therefore, it is suggested that the self-discharge behavior of V09Ti01 electrodes cannot be suppressed effectively by reduction of the plateau pressure of alloys through alloy modification.In addition, the pressure-composition-isotherms (P-C-T) of the low pressure region can be estimated by using the open-circuit potential corresponding to this region in Nernst’s equation.

The influence of aging at 180 °C on the corrosion behaviour of a ternary AlLiZr alloy

The influence of aging at 180 °C on the corrosion behaviour of an Al-1.5%Li-0.1%Zr alloy has been studied using weight loss, open circuit potential (OCP) measurements and potentiodynamic polarization measurements in 3.5% NaCl solution. Corrosion rates obtained from weight loss and I corr values decreased for samples aged up to 6 h at 180 °C whereas I corr increased for samples aged for longer times. Values of OCP and pitting potential initially shifted in the noble direction and then towards more active values. This change in OCP was observed on samples that had been aged for 20 h while in the case of pitting potential an aging time of only 6 h was required. The overall change in passive current density was small, although at longer aging times (> 40h) it showed an increase. As the amount of lithium depletion increased, OCP and pitting potential shifted in the active direction while passive current density showed an increase. The results have been interpreted in terms of the microstructure.

Open circuit potential for Copper Electrode in 1 M NaCl solutions

AbstractThe open circuit potential (OCP) of Cu electrode in 1 M NaCl solution was studied under different conditions. These include the change in pH (1–13), temperature (10–50°C) and the effect of O2, N2 and two organic additves, namely Sodium Methyl Dithiocarbamate and Sodium Butyl Dithiocarbamate. It was found that OCP changes to the positive or negative directions, depending on pH. The effect of temperature was found to depend mainly on pH. The presence of O2 has a pronounced effect on the potential and so is the addition of the two organic additives. The change of potential seems to be complicated since the kinetics of the change was found to be first, second or mixed first and second‐order depending on pH. The solid products formed at the electrode surface (pH = 1–9) were identified by IR spectroscopy.

On the electrochemical behaviour of aluminium in acidic chloride solution

The electrochemical behaviour of aluminium in 0.1 M hydrochloric acid solution positive of the open circuit potential (OCP) has been studied using open circuit potential measurements, linear sweep voltammetry and electrochemical impedance spectroscopy at stationary and rotating high purity aluminium disc electrodes. Freshly polished electrodes show an induction time before the OCP changes negatively towards its steady-state value. Steady-state current-voltage profiles show two distinct almost linear, non-Tafelian regions positive of the OCP. Evidence for pitting corrosion through a salt film and dissolution via ionic migration through the thin oxide film as parallel corrosion paths is discussed.

自然電位変化速度の測定による低合金鋼の焼き戻し脆化検出の検討

自然電位変化速度の測定による低合金鋼の焼き戻し脆化検出の検討

Evaluation of electrochemical properties for CrMoV steel in acidic solutions to determine embrittlement—I. Open circuit potential measurements in acidic aqueous solutions of various organic compounds

The embrittlement of CrMoV steel used for a steam turbine rotor, which had been in service over 139,000 h, has been investigated by open circuit potential measurements in acidic aqueous solutions of various organic compounds. The open circuit potential shifted positively in nitrophenol and nitrobenzoic acid solutions as the embrittlement level of the CrMoV steel increased, while it shifted negatively in aliphatic and aromatic acids without the nitro group. The possibility for embrittlement evaluation was also demonstrated by obtaining the rate of change in open circuit potential when solution stirring was stopped. The mechanism for the open circuit potential shift is discussed based on polarization measurements.

On some characteristics of cathodic processes in nickel electrodeposition

The potential of Ni2+-ion discharge at room temperature at first rapidly rises with an increase in pH of the solution, then within the pH range from 3·5 to 4·5 it decreases sharply, where-upon it again gradually begins to rise.Similar potential changes with an increase in pH are observed also in the case of a non-polarized electrode. For instance, the open-circuit potential of nickel in solutions of sulphuric acid and potassium sulphate rises linearly with an increase in pH to ca 3·5. Within the pH range from 3·5 to 4·7 the open-circuit potential changes considerably and its reproducibility is impaired. When the solution is made more alkaline within the pH range from 4·7 to ca 7·0, the increase in the potential becomes linear.By accurate measurements of pH in the vicinity of the cathode surface, it has been established that the changes in the potential of both non-polarized and polarized nickel electrodes observed are due to the regular changes in the acidity of the solution in the layer near the cathode.1 min after the immersion of a nickel electrode into the solution, the ΔpH in the vicinity of the electrode surface rises from 0·0 to 2·5, depending on the acidity of the medium. Upon cathodic polarization, pH rises to 7–8. But within the pH range from 3·5 to 4·5 an arrest in its increase is observed. The stepwise change in pH in the vicinity of the electrode surface and considerable changes in the potential are accounted for by the formation of basic nickel compounds and their adsorption on the electrode surface.